Molded products composed of (meth)acrylic resin compositions have excellent transparency and less optical strain and are therefore widely used as optical members such as lenses, prisms, phase difference films, light guide plates, light diffusion films, polarizing plate protective films and the like. In recent years, demands for lightweight and wide liquid crystal displays are high, and optical members are also required to be reduced in thickness and to be increased in area according to the demands. In addition, there is a demand for reproduction of highly fine images, and thereby a (meth)acrylic resin composition that is further less colored and has higher transparency is required.
The (meth)acrylic resin composition for optical members is usually mainly composed of a (meth)acrylic resin (also referred to as methacrylic polymer or (meth)acrylic polymer) produced by continuous bulk polymerization. For example, Patent Documents 1 and 2 each disclose a method of producing a methacrylic polymer. The method is characterized by continuously bulk polymerizing a monomer mixture comprising a radical polymerization initiator in an amount that is calculated from a calculation formula based on the half-life and concentration, discharging a polymer from the reactor at a specific polymer content, and continuously removing the volatile matters with a vent extruder. Patent Document 3 discloses a method of producing a (meth)acrylic polymer characterized by introducing an inert gas such as nitrogen gas into the shaft sealing portion of the vent extruder during the continuous removal of the volatile matter.